Can I Give My Dog Aspirin?

No
Aspirin causes stomach ulcers and bleeding in dogs, and it is no longer recommended now that safer canine NSAIDs exist. If a vet has not specifically told you to give it, skip it. One adult human tablet can be several times too much for a small dog.
Source: Pet Poison Helpline
Already ingested? Pet Poison Helpline 855-764-7661

The safe habit

Confirm any medication decision with your veterinarian, who knows your dog's health history and other medications. VetDose shows published reference data, not prescriptions.

See also

Other danger (no safe home dose) questions for dogs